Characteristics of seismic b-value of Changning shale gas region, Sichuan, derived from dense seismic array measurements

Exploitation of the shale gas in Changning area, Sichuan Province, is companied by numerous earthquakes including several moderate ones, and the seismic risk is increasing. With 241225 earthquakes detected, by a deep learning method, from the continuous records between May 2021 and June 2022 by a dense seismic array consisting of 107 stations in Changning area, we have estimated the b value in the frequency-magnitude relationship and analyzed its spatiotemporal characteristics. The b value for the whole area is 1.06; it is 1.25 and 1.01 for Changning-Shuanghe salt mining region and Changning-Zhaotong shale gas region, respectively. The low b value indicates that stress level in the shale gas region is higher. The b value remarkably varies in space and its variations are probably relative to the heterogeneity of the subsurface media. Basically, big earthquakes lie in low b-value regions, and the b-value appears low or drops before such events’ occurrence.